Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-09-21
2004-03-16
Epps, Georgia (Department: 2873)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231130, C250S231140
Reexamination Certificate
active
06707029
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a relative position measuring apparatus using an optical displacement measuring device. More particularly, the invention relates to a high accuracy relative position measuring apparatus that employs a linear optical encoder system comprising a glass scale and a light detecting sensor.
BACKGROUND ART
Laser-based measuring apparatuses using lasers and optical encoder-based measuring apparatuses using optical encoders are known in the art. The laser-based measuring apparatus can achieve high measurement accuracy as measurements are made using the laser light wavelength as the unit of measurement. The laser-based measuring apparatus is primarily used as a relative position measuring apparatus for measuring the length between two points. The optical encoder-based measuring apparatus comprises: a scale constructed from a glass plate, film, thin metal plate, or the like; an optical grid formed with a prescribed pitch on the scale; a fixed index grid disposed opposite the scale with prescribed spacing provided therebetween (the phase of the index grid is 90 degrees shifted relative to the phase of the optical grid); a fixed light source for illuminating the scale with collimated light; and a light detection sensor. When the scale moves, the optical grid and the index grid overlap each other, producing a pattern of light and dark. The light detection sensor detects this light and dark pattern. The optical encoder-based measuring apparatus is commercially implemented as a digital gauge, and is primarily used as a relative position measuring apparatus for measuring the distance between two points. Optical encoder-based measuring apparatus according to the prior art will be described below with reference to relevant drawings.
FIG. 21
is a diagram showing a first prior art. The measuring apparatus shown in
FIG. 21
comprises: a glass scale
10
; an optical grid
11
formed on the glass scale
10
; a light source
1
for illuminating the glass scale
10
with collimated slight; index grids
51
to
54
which receive light transmitted through the glass scale
10
; an index base
50
where the index grids
51
to
54
are formed; light receiving elements
61
to
64
for receiving light transmitted through the index grids
51
to
54
; and a substrate
20
where the light receiving elements
61
to
64
are formed. Also a semiconductor integrated circuit (IC)
22
and terminals
21
for connecting a cable
70
are formed on the substrate
20
.
The phase of the index grid
51
is shifted by
90
degrees, the phase of the index grid
52
is shifted by 180 degrees, the phase of the index grid
53
is shifted by 270 degrees, and the phase of index grid
54
is shifted by 360 degrees relative to the phase of the optical grid
11
. The light receiving elements
61
to
64
are each constructed from a signal light receiving element such as a photosensor.
The above-described first prior art is constructed by combining the glass scale, index grids, and light detection sensors, and thus the provision of index grids has been indispensable. Furthermore, to achieve high accuracy measurement, the pitch of the index grids, the proportions of the transparent and opaque portions of the index grids, the distance from the glass scale to the index grids, and the distance from the index grids to the light detection sensors must be adjusted accurately.
FIG. 22
is a diagram showing second prior art. The measuring apparatus shown in
FIG. 22
comprises: a glass scale
10
; an optical grid
11
formed on the glass scale
10
; a light source for illuminating the glass scale
10
with collimated light; a light receiving array
37
for receiving light transmitted through the glass scale
10
; and a substrate
20
where the light receiving array
37
is formed. Also a semiconductor integrated circuit (IC)
23
and terminals
21
for connecting a cable
70
are formed on the substrate
20
.
FIG. 23
is a diagram showing the relationship between the optical grid
11
and the light receiving array
37
in the second prior art. Reference character s designates the pitch of the optical grid
11
, while reference character w denotes the width of a transparent portion of the optical grid
11
and v denotes the width of an opaque portion of the optical grid
11
. Here, w and v are each set equal to s/2.
The light receiving array
37
consists of a plurality of light receiving elements. Reference character p designates the pitch of the light receiving elements, while reference character u denotes the width of a light receiving portion
35
and r denotes the width of a light insensitive portion. Here, p=3/4×s, u=s/2, and r=s/4. That is, the ratio of u to r is 2:1.
More specifically, the light receiving array
37
is arranged so that four light receiving elements, g
1
, g
2
, g
3
and g
4
, corresponds to three optical grid elements e
1
, e
2
and e
3
. Further, the light receiving array is constructed so that every fourth light receiving element receives the same amount of light.
In addition, a light receiving element a
1
is arranged so that its output is shifted in phase by 90 degrees relative to the output of b
1
, and a light receiving element b
1
is arranged so that its output is shifted in phase by 90 degrees relative to the output of c
1
. Likewise, c
1
and d
1
are arranged so that their outputs are shifted in phase by 90 degrees, respectively. In this arrangement, as shown in
FIG. 24
, every four light receiving elements are connected together and their outputs are summed. Here, let the sum of a
1
, a
2
, a
3
, . . . be denoted by A, the sum of b
1
, b
2
, b
3
, . . . denoted by B, the sum of c
1
, c
2
, c
3
, . . . denoted by C, and the sum of d
1
, d
2
, d
3
, . . . denoted by D. Then, the phases of A, B, C, and D are shifted by 90 degrees relative to one another. The measuring apparatus makes a measurement by processing the signals of A, B, C, and D.
As described above, in the second prior art, the size of each light receiving element has had to be restricted to 3/4×s, and complicated wiring has had to be provided to enable data to be taken from every four elements in the plurality of light receiving elements and summed together.
Another prior art is described in Japanese Unexamined Patent Publication Nos. 8-313209 and 9-33210. This prior art uses a light detection sensor (CCD) having sensor elements arranged in an array at the same pitch as the optical grid, and the light detection sensor is constructed to also serve as an index grid. In this prior art, however, since the light source is moved together with the optical grid while holding the light detection sensor stationary, the length of the light detection sensor (CCD) must be made equal to the measuring length.
Still another prior art is described in Japanese Unexamined Patent Publication 10-132612. In this prior art, light detection sensors are arranged so that they are shifted by s/4 relative to one another. This prior art, however, has the problem that the pitch of the optical grid is coarse and the resolution is low, since four light detection sensors must be arranged within one pitch of the optical grid.
It is an object of the present invention to provide a compact and high accuracy optical displacement measuring apparatus that resolves the above-outlined problems.
It is another object of the present invention to provide an optical displacement measuring apparatus that uses a plurality of light receiving arrays each having a plurality of light receiving elements arranged at the same pitch as the optical grid.
It is still another object of the present invention to provide an optical displacement measuring apparatus capable of indicating the unit of measurement (1 &mgr;m, 0.5 &mgr;m, etc) using simple configuration.
DISCLOSURE OF THE INVENTION
The present invention comprises: a moveable first member having an optical grid formed with a pitch s; a light source for illuminating the first member; a plurality of light receiving arrays, each having a plurality of light receiving
Citizen Watch Co. Ltd.
Epps Georgia
Harrington Alicia M
LandOfFree
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